1. Field of the Invention
The present invention relates to a charge pump circuit for generating an intermediate voltage between a power supply voltage and its double voltage.
2. Description of the Related Art
Recently, portable telephones, portable television game apparatuses and the like have been developed, and also, electronic apparatuses therefor have to be reduced in size and the power consumption thereof has to be reduced.
Generally, in a semiconductor integrated circuit consisting such an electronic apparatus, a single power supply voltage such as 5 V is used, and if a voltage higher than 5 V is required to drive a liquid crystal display panel or the like, a charge pump circuit as a step-up circuit is incorporated into the semiconductor integrated circuit. Note that a liquid crystal display panel requires a driving voltage of 6 V to 9 V dependent on the temperature thereof affecting the contrast of the display.
A prior art charge pump circuit is a switched capacitor type which includes two capacitors and four switches for charging the two capacitors using a single power supply voltage V.sub.DD to generate its double voltage 2 V.sub.DD (see: U.S. Pat. No. 4,807,104). In this prior art charge pump circuit, if an intermediate voltage between the power supply voltage V.sub.DD and its double voltage 2 V.sub.DD, an additional circuit including an operational amplifier is provided in the last stage of the charge pump circuit. This will be explained in more detail later.
In the above-mentioned charge pump circuit including the additional operational amplifier for an intermediate voltage, however, a large amount of power is consumed by the additional operational amplifier.